1. Field of the Invention
This invention relates to a developing device which is used in an image forming apparatus such as a copying machine, plotter, laser printer or facsimile machine. The invention further relates to the use of a seal which prevents toner from leaking and scattering.
2. Discussion of the Background
A conventional two step type of a developing device is shown in FIG. 7. The developing device includes an image bearing member 1 (e.g., a photosensitive drum), a first toner transporting roller 3, and a second toner transporting roller 2 which is provided between the image bearing member 1 and the first toner transporting roller 3. The first toner transporting roller 3 has a magnetic field generating layer which holds toner on the surface thereof. Additionally, there is a toner supplying roller 20 in contact with the first toner transporting roller 3.
There is a doctor blade 4 in contact with the first toner transporting roller 3. At a bottom portion of a developing hopper 5, there is a section 5a for storing and catching toner which extends under a lower side of the first toner transporting roller 3. A thickness of toner T which is held on the first toner transporting roller 3 is controlled by the doctor blade 4 which also charges the toner T using friction. The second toner transporting roller 2 is an elastic roller having a dielectric layer on its surface and is in contact with both the first toner transporting roller 3 and the image bearing member 1 so that predetermined contacting areas are formed on the rollers 2 and 3 and on the image bearing member 1.
The toner T is transferred from the first toner transporting roller 3 to the second toner transporting roller 2 by a bias voltage which is applied to the first toner transporting roller 3 using a voltage source/controller 24. The toner T which is transferred from the first toner transporting roller 3 is transferred from the second toner transporting roller 2 to a latent image on the image bearing member 1 which has been formed by a latent image forming device (not shown).
As shown in FIG. 8, to prevent toner from leaking, spilling out or scattering from the developing hopper in a two step type of a developing device, seals 6 are provided between the ends of the first toner transporting roller 3 and sides 7 of the developing hopper. However, as shown in FIGS. 9 and 10, there are slight non-contact portion(s) between the first toner transporting roller 3 and the second toner transporting roller 2; that is gaps A and A'. The collected toner gets in between the ends of the first toner transporting roller 3 and the sides and falls to the bottom portion 5a of the developing hopper from the gaps A and A' due to the rotation of the first toner transporting roller 3.
Further, since an agitator is provided in the developing hopper 5, toner flows out of and scatters around the developing hopper. Such seals 6 cannot effectively prevent toner from flowing out, spilling out, or scattering from the gaps A and A'.